Field of the Invention
The present invention relates to a lens array used for such a screen in an image display device, and an image display device including such lens array
Description of the Related Art
Conventionally, there is known ahead up display as an image display device showing a virtual image via a windshield to a passenger in a vehicle. And known as an example of such image display device is an image display device including alight source projecting light representing an image, and a transparent screen to which the light projected by the light source is irradiated, and utilizing a lens array as a screen s PTL 1 for example). This lens array is the one on which a plurality of convex lenses is bidimensionally-arranged along a predetermined reference face.
Here, known as what a structure similar to a lens array is included is a diffusion plate utilized for a reticle of a single lens reflex camera. The diffusion plate is the one in which a surface of such a glass plate is surface-roughened to provide micro concave-convex. In the case of utilizing such diffusion plate, size and arrangement of convex portions and concave portions on a surface thereon are so irregular that graininess like sand is shown on an image that the projecting light draws, possibly worsening an appearance of the image.
By contrast, in the case that a lens array where a plurality of convex lenses is bidimensionally regularly-arranged is utilized for the screen, such graininess as above on the image that the projecting light draws can hardly be seen due to regularity of lens arrangement. On the other hand, diffracted light due to cyclic structure of the lens array caused by the regularity of the lens arrangement occurs, likely inducing multiple lines blurring of iridescent on the image.
Accordingly, there has been proposed position in a plane view direction of vertex on each convex lens varied mutually among the plurality of convex lenses while the regularity of the lens arrangement remains unchanged (see PTL 2 for example) According to PTL 2, while assuring suppressing effect on graininess on the image due to the regularity of lens arrangement, varying position of vertex on each convex lens in the plane view direction as well, breaks cyclic structure of the lens array, suppressing multiple lines blurring of iridescent due to diffracted light.
Disadvantageously, according to the technology of the abovementioned PTL 2, varying the positions of vertex on each convex lens in order to suppress multiple lines blurring of iridescent by diffracted light also breaks the regularity of lens arrangement. For this reason, in order to further suppress the multiple lines blurring of the iridescent, broadening the variation of the vertex position of each convex lens may not in return be able to suppress the graininess.